Origin of the increased velocities of domain wall motions in soft magnetic thin-film nanostripes beyond the velocity-breakdown regime

TL;DR

This paper investigates the unexpected increase in domain wall velocities in soft magnetic nanostripes beyond the velocity-breakdown regime, attributing it to vortex-antivortex dynamics and nonlinear processes.

Contribution

It reveals the physical mechanism behind increased domain wall velocities beyond the velocity-breakdown regime, emphasizing the role of vortex-antivortex nucleation and nonlinear gyrotropic motions.

Findings

Vortex-antivortex pairs nucleate inside or at edges of the stripe.

Nonlinear gyrotropic motions of vortices and antivortices occur.

A two-dimensional soliton model explains the observed behaviors.

Abstract

It is known that oscillatory domain-wall (DW) motions in soft magnetic thin-film nanostripes above the Walker critical field lead to a remarkable reduction in the average DW velocities. In a much-higher-field region beyond the velocity-breakdown regime, however, the DW velocities have been found to increase in response to a further increase of the applied field. We report on the physical origin and detailed mechanism of this unexpected behavior. We associate the mechanism with the serial dynamic processes of the nucleation of vortex-antivortex (V-AV) pairs inside the stripe or at its edges, the non-linear gyrotropic motions of Vs and AVs, and their annihilation process. The present results imply that a two-dimensional soliton model is required for adequate interpretation of DW motions in the linear- and oscillatory-DW-motion regimes as well as in the beyond-velocity-breakdown regime.